Evaluation of Monochloramine and Free Chlorine Penetration in a Drinking Water Storage Tank Sediment Using Microelectrodes

Sediment accumulation in water storage tanks may protect microorganisms from disinfectant exposure, causing water quality degradation. However, microbial activity and disinfectant penetration within water storage sediment remains largely uncharacterized. This study evaluated monochloramine and free chlorine penetration into a 2-cm (20,000 µm) deep drinking water storage tank sediment using microelectrodes. The sediment was successively exposed to 4-months monochloramine, 2-months free chlorine, and 2-months monochloramine. Temporal monochloramine, free chlorine, dissolved oxygen (DO), pH, ammonium, nitrite, and nitrate profiles were acquired using microelectrodes. Results showed that complete monochloramine or free chlorine penetration was not observed. Likewise, DO never fully penetrated the sediment, progressing inward with time to a maximum depth of 10,000 µm and indicating microbial activity remained during the entire 8 months. Decreasing ammonium and increasing nitrate concentrations, with minimal nitrite accumulation, further demonstrated microbial activity and indicated complete sediment nitrification. There was measurable ammonium, nitrite, and nitrate during free chlorine application and nitrification activity gradually resumed upon a switch back to monochloramine. These findings suggest that periodic sediment removal from drinking water storage facilities is desirable to remove potentially protected environments for microorganisms.

This dataset is associated with the following publication:
Liu, H., D. Wahman, and J. Pressman. Evaluation of Monochloramine and Free Chlorine Penetration in a Drinking Water Storage Tank Sediment Using Microelectrodes. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, USA, 53(16): 9352-9360, (2019).